The optical frequency comb （OFC） generation of 2 μm silicon nitride microcavity is investigated. Dispersion modulation of silicon nitride waveguides is carried out by geometrical design. Appropriate bus waveguide dimensions are selected， and the thermal refraction noise of silicon nitride microcavities at different modulation frequencies is discussed by the thermal absorption theory. The nonlinear Schr?dinger equation is used as the basic model to study the evolution of the cavity under different dispersion effects. The numerical results show that silicon nitride is able to observe the hysteretic state transition of the system， i.e.， the relaxation oscillation phenomenon during the transition of the system to the stable domain， more clearly in the 2 μm band. At the same time， the cavity is able to transition to the steady state soliton faster under the action of higher-order dispersion， which provides a scheme to study the respiratory soliton.